Fix tolerance problem in matlab FaustTest.testcat.

It happened rarely:
Verification failed in FaustTest/testcat.

    ---------------------
    Framework Diagnostic:
    ---------------------
    verifyEqual failed.
    --> The values are not equal using isequaln.
    --> The error was not within absolute tolerance.
    --> Failure table:
            Index     Subscripts        Actual             Expected              Error              RelativeError        AbsoluteTolerance
            ______    __________    _______________    ________________    _________________    _____________________    _________________

            110629    (517,187)     342279799020.63    342279799020.631    -0.00115966796875    -3.38807014631939e-15          0.001

    Actual Value:
        592x507 double
    Expected Value:
        592x507 double

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    Stack Information:
    ------------------
    In /Users/ci/builds/Z-XUzYP3/0/faustgrp/faust/misc/test/src/Matlab/FaustTest.m (FaustTest.testcat) at 582